As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks to brightest brights. In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
As used herein, the terms extended dynamic range or high dynamic range (HDR) relates to a DR breadth that spans the some 14-15 orders of magnitude of the human visual system (HVS). For example, well adapted humans with essentially normal (e.g., in one or more of a statistical, biometric or opthamological sense) have an intensity range that spans about 15 orders of magnitude. Adapted humans may perceive dim light sources of as few as a mere handful of photons. Yet, these same humans may perceive the near painfully brilliant intensity of the noonday sun in desert, sea or snow (or even glance into the sun, however briefly to prevent damage). This span though is available to ‘adapted’ humans, e.g., those whose HVS has a time period in which to reset and adjust.
In contrast, the DR over which a human may simultaneously perceive an extensive breadth in intensity range may be somewhat truncated, in relation to HDR. As used herein, the terms ‘visual dynamic range’ or ‘variable dynamic range’ (VDR) may individually or interchangeably relate to the DR that is simultaneously perceivable by a HVS. As used herein, VDR may relate to a DR that spans 5-6 orders of magnitude. Thus while perhaps somewhat narrower in relation to true scene referred HDR, VDR nonetheless represents a wide DR breadth. Despite the DR differences between HDR and VDR images, as used herein, the term VDR may be used to characterize any image with an extended dynamic range.
Until fairly recently, displays have had a significantly narrower DR than HDR or VDR. Television (TV) and computer monitor apparatus that use typical cathode ray tube (CRT), liquid crystal display (LCD) with constant fluorescent white back lighting or plasma screen technology may be constrained in their DR rendering capability to approximately three orders of magnitude. Such conventional displays thus typify a low dynamic range (LDR), also referred to as a standard dynamic range (SDR), in relation to VDR and HDR.
In image processing applications, given two m×n images I and Î, where Î is considered an approximation of image I, the peak signal to noise ratio (PSNR) is commonly defined as
                                          PSNR            (                          I              ,                              I                ^                                      )                    =                                    10              ⁢                              log                ⁡                                  (                                                            max                      I                      2                                                              MSE                      (                                              I                        ,                                                  I                          ^                                                                    )                                                        )                                                      =                                          -                10                            ⁢                              log                (                                                      MSE                    (                                          I                      ,                                              I                        ^                                                              )                                                        max                    I                    2                                                  )                                                    ,                                  ⁢        where        ,                            (        1        )                                                      MSE            ⁢                          (                              I                ,                                  I                  ^                                            )                                =                                    1              mn                        ⁢                                          ∑                                  i                  =                  0                                                  m                  -                  1                                            ⁢                                                ∑                                      j                    =                    0                                                        n                    -                    1                                                  ⁢                                                      (                                                                  I                        ⁡                                                  (                                                      i                            ,                            j                                                    )                                                                    -                                                                        I                          ^                                                ⁡                                                  (                                                      i                            ,                            j                                                    )                                                                                      )                                    2                                                                    ,                            (        2        )            denotes the mean square error (MSE) between the two images and max/denotes the maximum possible pixel value in one of the color components of image I. For example, for monochrome images represented with N bits per pixel max=2N−1.
Color images may be represented with multiple color components (e.g., RGB, YCbCr, or similar representations). For color images, a separate PSNR value may be computed for every color component of interest and these values may be added or averaged together. Without loss of generality, and for simplicity and brevity in what follows, quality assessment is described for a single color component of an image in a multi-component representation (e.g., RGB or YCbCr).
In image coding, PSNR is commonly used as a simple, but objective, measure of quality, wherein Î typically represents a reconstructed approximation of image I, after image I has been coded using an image or video coding algorithm, such as those defined by the joint pictures expert group (JPEG) or the motion pictures experts group (MPEG).
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.